The last thing the NHS needs is a large reform as it is one of the world's best health systems and has been improving patient care for years, says the author of the OECD's flagship report into international care and treatment.

The report by the Organisation for Economic Co-operation and Development thinktank, which is funded by wealthy governments, says the NHS has cut heart attack deaths by two-thirds since 1980; the public rarely has to pay to meet health needs; and citizens have comparable life expectancies to their neighbours on the continent. Among global diseases the UK also scores well: less than 5% of adults had diabetes in 2010, contrasting with 10% in the United States.

"The UK is one of the best performers in the world. But outcomes are not what you expect because there is a big reform every five years. We calculate that each reform costs two years of improvements in quality. No country reforms its health service as frequently as the UK," said Mark Pearson, head of health at the OECD.

When it was put to Pearson, a respected economist, that the NHS faces its biggest upheaval in 60 years with the coalition's health bill, he said: "The NHS is so central to the political process that every politician has to promise to improve the NHS. But there's no big reform that will improve it. Better to let it bed down and tinker rather than wondering about more or less competition. It is less the type of system that counts, but rather how it is managed."

However, the OECD does point out that mortality rates in breast, prostate, cervical and bowel cancer were higher than the developed world's average in 2009. For all cancers combined, the UK ranked 16th out of the 34 countries when it came to death rates. There were also more avoidable hospital admissions for asthma in the UK than the average. Typically, 52 out of 100,000 adults in OECD countries are admitted to hospital for asthma each year. In the UK, the figure is 74. Pearson said this could be down to "poor air quality".

The report highlighted the prevalence of drinking and obesity, which would, if unchecked, lead to "long-term problems, especially in the labour market, which could affect growth".

One feature was the high pay of British GPs – who take home 3.6 times the average salary, the second biggest multiple in the developed world. The NHS also ran a tight ship financially, which meant the UK had very few CT scanners: "There are absurd amounts of these in Greece, Japan and the US. Frankly most are not used."

Waiting times had come down dramatically under Labour – and the OECD had concerns about recent evidence that suggested patients were not being seen as quickly as before. In 2005, 60% of patients waited four weeks to see a specialist. By 2010 that was down to 28% – better than Sweden, the Netherlands and France.

The report also noted the large proportion of the over-50s looking after family – in the UK, 15% of those in this age group reported themselves "carers", almost double some Nordic countries. Pearson warned that having no "institutional set-up" to deal with social care would extract a high economic price – "Caring for family reduces a worker's pay, their hours of work, affects their health. It's a cost."

Andrew Lansley, the health secretary, argued the report made the case for reform. "It clearly shows that although the NHS is doing well in some areas, it is still lagging behind other countries in some key areas of patient care. Improving patient results is a top priority for me. We need to allow the NHS to focus on what really matters to patients; things like survival rates, recovery rates and whether people can live independently and with dignity."

Labour claimed that Lansley was "desperately talking down the NHS to justify his ill-conceived bill". The party's health spokesman, Andy Burnham, said: "This report confirms what others have been saying. The OECD, and the recent Commonwealth Fund report too, say that Britain has one of the best health services in the world, which begs the simple question, why is the government intent on turning it upside down and putting the progress at risk?"